1. Field of the Invention
The present invention relates to elastic wave filter devices used in transmission and reception.
2. Description of the Related Art
As a conventional elastic wave filter device, a duplexer disclosed in Japanese Unexamined Patent Application Publication No. 2007-67617 can be cited, for example. This duplexer includes a transmission piezoelectric filter formed on a first substrate and a reception piezoelectric filter formed on a second substrate. The first substrate and the second substrate are disposed such that the transmission piezoelectric filter and the reception piezoelectric filter oppose each other. An interspace between the first substrate and the second substrate is air-tightly sealed with an outer periphery pad. The duplexer is mounted on a mother substrate while setting the transmission piezoelectric filter side to be a lower surface of the duplexer, thereby improving heat dissipation effects.
In general, reception filters are required to have high-level attenuation characteristics, particularly at transmission wave bands, in order to suppress wraparound action of the transmission waves. As for the duplexer disclosed in Japanese Unexamined Patent Application Publication No. 2007-67617, it is mounted on the mother substrate such that the reception piezoelectric filter is disposed on a side being distanced from the mother substrate. Because of this, a wiring length between the reception piezoelectric filter and a ground line of the mother substrate becomes long. As a result, a stray inductance is generated between the reception piezoelectric filter and the ground line, wiring resistance increases, and so on. This consequently degrades attenuation characteristics of the reception filter.